src/common/fd-tracker/fd-tracker.c

   1 /*
   2  * Copyright (C) 2018 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
   3  *
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License, version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
  11  * more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along with
  14  * this program; if not, write to the Free Software Foundation, Inc., 51
  15  * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  16  */
  17
  18 #include <urcu.h>
  19 #include <urcu/list.h>
  20 #include <urcu/rculfhash.h>
  21
  22 #include <fcntl.h>
  23 #include <inttypes.h>
  24 #include <pthread.h>
  25 #include <stdbool.h>
  26 #include <sys/stat.h>
  27 #include <sys/types.h>
  28
  29 #include "common/defaults.h"
  30 #include "common/error.h"
  31 #include "common/hashtable/hashtable.h"
  32 #include "common/hashtable/utils.h"
  33 #include "common/macros.h"
  34
  35 #include "fd-tracker.h"
  36 #include "inode.h"
  37
  38 /* Tracker lock must be taken by the user. */
  39 #define TRACKED_COUNT(tracker)                                 \
  40         (tracker->count.suspendable.active +                   \
  41                         tracker->count.suspendable.suspended + \
  42                         tracker->count.unsuspendable)
  43
  44 /* Tracker lock must be taken by the user. */
  45 #define ACTIVE_COUNT(tracker) \
  46         (tracker->count.suspendable.active + tracker->count.unsuspendable)
  47
  48 /* Tracker lock must be taken by the user. */
  49 #define SUSPENDED_COUNT(tracker) (tracker->count.suspendable.suspended)
  50
  51 /* Tracker lock must be taken by the user. */
  52 #define SUSPENDABLE_COUNT(tracker)           \
  53         (tracker->count.suspendable.active + \
  54                         tracker->count.suspendable.suspended)
  55
  56 /* Tracker lock must be taken by the user. */
  57 #define UNSUSPENDABLE_COUNT(tracker) (tracker->count.unsuspendable)
  58
  59 struct fd_tracker {
  60         pthread_mutex_t lock;
  61         struct {
  62                 struct {
  63                         unsigned int active;
  64                         unsigned int suspended;
  65                 } suspendable;
  66                 unsigned int unsuspendable;
  67         } count;
  68         unsigned int capacity;
  69         struct {
  70                 uint64_t uses;
  71                 uint64_t misses;
  72                 /* Failures to suspend or restore fs handles. */
  73                 uint64_t errors;
  74         } stats;
  75         /*
  76          * The head of the active_handles list is always the least recently
  77          * used active handle. When an handle is used, it is removed from the
  78          * list and added to the end. When a file has to be suspended, the
  79          * first element in the list is "popped", suspended, and added to the
  80          * list of suspended handles.
  81          */
  82         struct cds_list_head active_handles;
  83         struct cds_list_head suspended_handles;
  84         struct cds_lfht *unsuspendable_fds;
  85         struct lttng_inode_registry *inode_registry;
  86 };
  87
  88 struct open_properties {
  89         int flags;
  90         struct {
  91                 bool is_set;
  92                 mode_t value;
  93         } mode;
  94 };
  95
  96 /*
  97  * A fs_handle is not ref-counted. Therefore, it is assumed that a
  98  * handle is never in-use while it is being reclaimed. It can be
  99  * shared by multiple threads, but external synchronization is required
 100  * to ensure it is not still being used when it is reclaimed (close method).
 101  * In this respect, it is not different from a regular file descriptor.
 102  *
 103  * The fs_handle lock always nests _within_ the tracker's lock.
 104  */
 105 struct fs_handle {
 106         pthread_mutex_t lock;
 107         /*
 108          * Weak reference to the tracker. All fs_handles are assumed to have
 109          * been closed at the moment of the destruction of the fd_tracker.
 110          */
 111         struct fd_tracker *tracker;
 112         struct open_properties properties;
 113         struct lttng_inode *inode;
 114         int fd;
 115         /* inode number of the file at the time of the handle's creation. */
 116         uint64_t ino;
 117         bool in_use;
 118         /* Offset to which the file should be restored. */
 119         off_t offset;
 120         struct cds_list_head handles_list_node;
 121 };
 122
 123 struct unsuspendable_fd {
 124         /*
 125          * Accesses are only performed through the tracker, which is protected
 126          * by its own lock.
 127          */
 128         int fd;
 129         char *name;
 130         struct cds_lfht_node tracker_node;
 131         struct rcu_head rcu_head;
 132 };
 133
 134 static struct {
 135         pthread_mutex_t lock;
 136         bool initialized;
 137         unsigned long value;
 138 } seed = {
 139         .lock = PTHREAD_MUTEX_INITIALIZER,
 140 };
 141
 142 static int match_fd(struct cds_lfht_node *node, const void *key);
 143 static void unsuspendable_fd_destroy(struct unsuspendable_fd *entry);
 144 static struct unsuspendable_fd *unsuspendable_fd_create(
 145                 const char *name, int fd);
 146 static int open_from_properties(
 147                 const char *path, struct open_properties *properties);
 148
 149 static void fs_handle_log(struct fs_handle *handle);
 150 static int fs_handle_suspend(struct fs_handle *handle);
 151 static int fs_handle_restore(struct fs_handle *handle);
 152
 153 static void fd_tracker_track(
 154                 struct fd_tracker *tracker, struct fs_handle *handle);
 155 static void fd_tracker_untrack(
 156                 struct fd_tracker *tracker, struct fs_handle *handle);
 157 static int fd_tracker_suspend_handles(
 158                 struct fd_tracker *tracker, unsigned int count);
 159 static int fd_tracker_restore_handle(
 160                 struct fd_tracker *tracker, struct fs_handle *handle);
 161
 162 /* Match function of the tracker's unsuspendable_fds hash table. */
 163 static int match_fd(struct cds_lfht_node *node, const void *key)
 164 {
 165         struct unsuspendable_fd *entry = caa_container_of(
 166                         node, struct unsuspendable_fd, tracker_node);
 167
 168         return hash_match_key_ulong(
 169                         (void *) (unsigned long) entry->fd, (void *) key);
 170 }
 171
 172 static void delete_unsuspendable_fd(struct rcu_head *head)
 173 {
 174         struct unsuspendable_fd *fd = caa_container_of(
 175                         head, struct unsuspendable_fd, rcu_head);
 176
 177         free(fd->name);
 178         free(fd);
 179 }
 180
 181 static void unsuspendable_fd_destroy(struct unsuspendable_fd *entry)
 182 {
 183         if (!entry) {
 184                 return;
 185         }
 186         call_rcu(&entry->rcu_head, delete_unsuspendable_fd);
 187 }
 188
 189 static struct unsuspendable_fd *unsuspendable_fd_create(
 190                 const char *name, int fd)
 191 {
 192         struct unsuspendable_fd *entry = zmalloc(sizeof(*entry));
 193
 194         if (!entry) {
 195                 goto error;
 196         }
 197         if (name) {
 198                 entry->name = strdup(name);
 199                 if (!entry->name) {
 200                         goto error;
 201                 }
 202         }
 203         cds_lfht_node_init(&entry->tracker_node);
 204         entry->fd = fd;
 205         return entry;
 206 error:
 207         unsuspendable_fd_destroy(entry);
 208         return NULL;
 209 }
 210
 211 static void fs_handle_log(struct fs_handle *handle)
 212 {
 213         const char *path;
 214
 215         pthread_mutex_lock(&handle->lock);
 216         path = lttng_inode_get_path(handle->inode);
 217
 218         if (handle->fd >= 0) {
 219                 DBG_NO_LOC("    %s [active, fd %d%s]", path, handle->fd,
 220                                 handle->in_use ? ", in use" : "");
 221         } else {
 222                 DBG_NO_LOC("    %s [suspended]", path);
 223         }
 224         pthread_mutex_unlock(&handle->lock);
 225 }
 226
 227 /* Tracker lock must be held by the caller. */
 228 static int fs_handle_suspend(struct fs_handle *handle)
 229 {
 230         int ret = 0;
 231         struct stat fs_stat;
 232         const char *path;
 233
 234         pthread_mutex_lock(&handle->lock);
 235         path = lttng_inode_get_path(handle->inode);
 236         assert(handle->fd >= 0);
 237         if (handle->in_use) {
 238                 /* This handle can't be suspended as it is currently in use. */
 239                 ret = -EAGAIN;
 240                 goto end;
 241         }
 242
 243         ret = stat(path, &fs_stat);
 244         if (ret) {
 245                 PERROR("Filesystem handle to %s cannot be suspended as stat() failed",
 246                                 path);
 247                 ret = -errno;
 248                 goto end;
 249         }
 250
 251         if (fs_stat.st_ino != handle->ino) {
 252                 /* Don't suspend as the handle would not be restorable. */
 253                 WARN("Filesystem handle to %s cannot be suspended as its inode changed",
 254                                 path);
 255                 ret = -ENOENT;
 256                 goto end;
 257         }
 258
 259         handle->offset = lseek(handle->fd, 0, SEEK_CUR);
 260         if (handle->offset == -1) {
 261                 WARN("Filesystem handle to %s cannot be suspended as lseek() failed to sample its current position",
 262                                 path);
 263                 ret = -errno;
 264                 goto end;
 265         }
 266
 267         ret = close(handle->fd);
 268         if (ret) {
 269                 PERROR("Filesystem handle to %s cannot be suspended as close() failed",
 270                                 path);
 271                 ret = -errno;
 272                 goto end;
 273         }
 274         DBG("Suspended filesystem handle to %s (fd %i) at position %" PRId64,
 275                         path, handle->fd, handle->offset);
 276         handle->fd = -1;
 277 end:
 278         if (ret) {
 279                 handle->tracker->stats.errors++;
 280         }
 281         pthread_mutex_unlock(&handle->lock);
 282         return ret;
 283 }
 284
 285 /* Caller must hold the tracker and handle's locks. */
 286 static int fs_handle_restore(struct fs_handle *handle)
 287 {
 288         int ret, fd = -1;
 289         const char *path = lttng_inode_get_path(handle->inode);
 290
 291         assert(handle->fd == -1);
 292         assert(path);
 293         ret = open_from_properties(path, &handle->properties);
 294         if (ret < 0) {
 295                 PERROR("Failed to restore filesystem handle to %s, open() failed",
 296                                 path);
 297                 ret = -errno;
 298                 goto end;
 299         }
 300         fd = ret;
 301
 302         ret = lseek(fd, handle->offset, SEEK_SET);
 303         if (ret < 0) {
 304                 PERROR("Failed to restore filesystem handle to %s, lseek() failed",
 305                                 path);
 306                 ret = -errno;
 307                 goto end;
 308         }
 309         DBG("Restored filesystem handle to %s (fd %i) at position %" PRId64,
 310                         path, fd, handle->offset);
 311         ret = 0;
 312         handle->fd = fd;
 313         fd = -1;
 314 end:
 315         if (fd >= 0) {
 316                 (void) close(fd);
 317         }
 318         return ret;
 319 }
 320
 321 static int open_from_properties(
 322                 const char *path, struct open_properties *properties)
 323 {
 324         int ret;
 325
 326         /*
 327          * open() ignores the 'flags' parameter unless the O_CREAT or O_TMPFILE
 328          * flags are set. O_TMPFILE would not make sense in the context of a
 329          * suspendable fs_handle as it would not be restorable (see OPEN(2)),
 330          * thus it is ignored here.
 331          */
 332         if ((properties->flags & O_CREAT) && properties->mode.is_set) {
 333                 ret = open(path, properties->flags, properties->mode.value);
 334         } else {
 335                 ret = open(path, properties->flags);
 336         }
 337         /*
 338          * Some flags should not be used beyond the initial open() of a
 339          * restorable file system handle. O_CREAT and O_TRUNC must
 340          * be cleared since it would be unexpected to re-use them
 341          * when the handle is retored:
 342          *  - O_CREAT should not be needed as the file has been created
 343          *    on the initial call to open(),
 344          *  - O_TRUNC would destroy the file's contents by truncating it
 345          *    to length 0.
 346          */
 347         properties->flags &= ~(O_CREAT | O_TRUNC);
 348         if (ret < 0) {
 349                 ret = -errno;
 350                 goto end;
 351         }
 352 end:
 353         return ret;
 354 }
 355
 356 struct fd_tracker *fd_tracker_create(unsigned int capacity)
 357 {
 358         struct fd_tracker *tracker = zmalloc(sizeof(struct fd_tracker));
 359
 360         if (!tracker) {
 361                 goto end;
 362         }
 363
 364         pthread_mutex_lock(&seed.lock);
 365         if (!seed.initialized) {
 366                 seed.value = (unsigned long) time(NULL);
 367                 seed.initialized = true;
 368         }
 369         pthread_mutex_unlock(&seed.lock);
 370
 371         CDS_INIT_LIST_HEAD(&tracker->active_handles);
 372         CDS_INIT_LIST_HEAD(&tracker->suspended_handles);
 373         tracker->capacity = capacity;
 374         tracker->unsuspendable_fds = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
 375                         CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
 376         if (!tracker->unsuspendable_fds) {
 377                 ERR("Failed to create fd-tracker's unsuspendable_fds hash table");
 378                 goto error;
 379         }
 380         tracker->inode_registry = lttng_inode_registry_create();
 381         if (!tracker->inode_registry) {
 382                 ERR("Failed to create fd-tracker's inode registry");
 383                 goto error;
 384         }
 385         DBG("File descriptor tracker created with a limit of %u simultaneously-opened FDs",
 386                         capacity);
 387 end:
 388         return tracker;
 389 error:
 390         fd_tracker_destroy(tracker);
 391         return NULL;
 392 }
 393
 394 void fd_tracker_log(struct fd_tracker *tracker)
 395 {
 396         struct fs_handle *handle;
 397         struct unsuspendable_fd *unsuspendable_fd;
 398         struct cds_lfht_iter iter;
 399
 400         pthread_mutex_lock(&tracker->lock);
 401         DBG_NO_LOC("File descriptor tracker");
 402         DBG_NO_LOC("  Stats:");
 403         DBG_NO_LOC("    uses:            %" PRIu64, tracker->stats.uses);
 404         DBG_NO_LOC("    misses:          %" PRIu64, tracker->stats.misses);
 405         DBG_NO_LOC("    errors:          %" PRIu64, tracker->stats.errors);
 406         DBG_NO_LOC("  Tracked:           %u", TRACKED_COUNT(tracker));
 407         DBG_NO_LOC("    active:          %u", ACTIVE_COUNT(tracker));
 408         DBG_NO_LOC("      suspendable:   %u", SUSPENDABLE_COUNT(tracker));
 409         DBG_NO_LOC("      unsuspendable: %u", UNSUSPENDABLE_COUNT(tracker));
 410         DBG_NO_LOC("    suspended:       %u", SUSPENDED_COUNT(tracker));
 411         DBG_NO_LOC("    capacity:        %u", tracker->capacity);
 412
 413         DBG_NO_LOC("  Tracked suspendable file descriptors");
 414         cds_list_for_each_entry (
 415                         handle, &tracker->active_handles, handles_list_node) {
 416                 fs_handle_log(handle);
 417         }
 418         cds_list_for_each_entry (handle, &tracker->suspended_handles,
 419                         handles_list_node) {
 420                 fs_handle_log(handle);
 421         }
 422         if (!SUSPENDABLE_COUNT(tracker)) {
 423                 DBG_NO_LOC("    None");
 424         }
 425
 426         DBG_NO_LOC("  Tracked unsuspendable file descriptors");
 427         rcu_read_lock();
 428         cds_lfht_for_each_entry (tracker->unsuspendable_fds, &iter,
 429                         unsuspendable_fd, tracker_node) {
 430                 DBG_NO_LOC("    %s [active, fd %d]",
 431                                 unsuspendable_fd->name ?: "Unnamed",
 432                                 unsuspendable_fd->fd);
 433         }
 434         rcu_read_unlock();
 435         if (!UNSUSPENDABLE_COUNT(tracker)) {
 436                 DBG_NO_LOC("    None");
 437         }
 438
 439         pthread_mutex_unlock(&tracker->lock);
 440 }
 441
 442 int fd_tracker_destroy(struct fd_tracker *tracker)
 443 {
 444         int ret = 0;
 445
 446         /*
 447          * Refuse to destroy the tracker as fs_handles may still old
 448          * weak references to the tracker.
 449          */
 450         pthread_mutex_lock(&tracker->lock);
 451         if (TRACKED_COUNT(tracker)) {
 452                 ERR("A file descriptor leak has been detected: %u tracked file descriptors are still being tracked",
 453                                 TRACKED_COUNT(tracker));
 454                 pthread_mutex_unlock(&tracker->lock);
 455                 fd_tracker_log(tracker);
 456                 ret = -1;
 457                 goto end;
 458         }
 459         pthread_mutex_unlock(&tracker->lock);
 460
 461         if (tracker->unsuspendable_fds) {
 462                 ret = cds_lfht_destroy(tracker->unsuspendable_fds, NULL);
 463                 assert(!ret);
 464         }
 465
 466         lttng_inode_registry_destroy(tracker->inode_registry);
 467         pthread_mutex_destroy(&tracker->lock);
 468         free(tracker);
 469 end:
 470         return ret;
 471 }
 472
 473 struct fs_handle *fd_tracker_open_fs_handle(struct fd_tracker *tracker,
 474                 const char *path,
 475                 int flags,
 476                 mode_t *mode)
 477 {
 478         int ret;
 479         struct fs_handle *handle = NULL;
 480         struct stat fd_stat;
 481         struct open_properties properties = {
 482                 .flags = flags,
 483                 .mode.is_set = !!mode,
 484                 .mode.value = mode ? *mode : 0,
 485         };
 486
 487         pthread_mutex_lock(&tracker->lock);
 488         if (ACTIVE_COUNT(tracker) == tracker->capacity) {
 489                 if (tracker->count.suspendable.active > 0) {
 490                         ret = fd_tracker_suspend_handles(tracker, 1);
 491                         if (ret) {
 492                                 goto end;
 493                         }
 494                 } else {
 495                         /*
 496                          * There are not enough active suspendable file
 497                          * descriptors to open a new fd and still accommodate
 498                          * the tracker's capacity.
 499                          */
 500                         WARN("Cannot open file system handle, too many unsuspendable file descriptors are opened (%u)",
 501                                         tracker->count.unsuspendable);
 502                         goto end;
 503                 }
 504         }
 505
 506         handle = zmalloc(sizeof(*handle));
 507         if (!handle) {
 508                 goto end;
 509         }
 510         handle->tracker = tracker;
 511
 512         ret = pthread_mutex_init(&handle->lock, NULL);
 513         if (ret) {
 514                 PERROR("Failed to initialize handle mutex while creating fs handle");
 515                 goto error_mutex_init;
 516         }
 517
 518         handle->fd = open_from_properties(path, &properties);
 519         if (handle->fd < 0) {
 520                 PERROR("Failed to open fs handle to %s, open() returned", path);
 521                 goto error;
 522         }
 523
 524         handle->properties = properties;
 525
 526         handle->inode = lttng_inode_registry_get_inode(
 527                         tracker->inode_registry, handle->fd, path);
 528         if (!handle->inode) {
 529                 ERR("Failed to get lttng_inode corresponding to file %s", path);
 530                 goto error;
 531         }
 532
 533         if (fstat(handle->fd, &fd_stat)) {
 534                 PERROR("Failed to retrieve file descriptor inode while creating fs handle, fstat() returned");
 535                 goto error;
 536         }
 537         handle->ino = fd_stat.st_ino;
 538
 539         fd_tracker_track(tracker, handle);
 540 end:
 541         pthread_mutex_unlock(&tracker->lock);
 542         return handle;
 543 error:
 544         if (handle->inode) {
 545                 lttng_inode_put(handle->inode);
 546         }
 547         pthread_mutex_destroy(&handle->lock);
 548 error_mutex_init:
 549         free(handle);
 550         handle = NULL;
 551         goto end;
 552 }
 553
 554 /* Caller must hold the tracker's lock. */
 555 static int fd_tracker_suspend_handles(
 556                 struct fd_tracker *tracker, unsigned int count)
 557 {
 558         unsigned int left_to_close = count;
 559         struct fs_handle *handle, *tmp;
 560
 561         cds_list_for_each_entry_safe (handle, tmp, &tracker->active_handles,
 562                         handles_list_node) {
 563                 int ret;
 564
 565                 fd_tracker_untrack(tracker, handle);
 566                 ret = fs_handle_suspend(handle);
 567                 fd_tracker_track(tracker, handle);
 568                 if (!ret) {
 569                         left_to_close--;
 570                 }
 571
 572                 if (!left_to_close) {
 573                         break;
 574                 }
 575         }
 576         return left_to_close ? -EMFILE : 0;
 577 }
 578
 579 int fd_tracker_open_unsuspendable_fd(struct fd_tracker *tracker,
 580                 int *out_fds,
 581                 const char **names,
 582                 unsigned int fd_count,
 583                 fd_open_cb open,
 584                 void *user_data)
 585 {
 586         int ret, user_ret, i, fds_to_suspend;
 587         unsigned int active_fds;
 588         struct unsuspendable_fd *entries[fd_count];
 589
 590         memset(entries, 0, sizeof(entries));
 591
 592         pthread_mutex_lock(&tracker->lock);
 593
 594         active_fds = ACTIVE_COUNT(tracker);
 595         fds_to_suspend = (int) active_fds + (int) fd_count -
 596                         (int) tracker->capacity;
 597         if (fds_to_suspend > 0) {
 598                 if (fds_to_suspend <= tracker->count.suspendable.active) {
 599                         ret = fd_tracker_suspend_handles(
 600                                         tracker, fds_to_suspend);
 601                         if (ret) {
 602                                 goto end;
 603                         }
 604                 } else {
 605                         /*
 606                          * There are not enough active suspendable file
 607                          * descriptors to open a new fd and still accomodate the
 608                          * tracker's capacity.
 609                          */
 610                         WARN("Cannot open unsuspendable fd, too many unsuspendable file descriptors are opened (%u)",
 611                                         tracker->count.unsuspendable);
 612                         ret = -EMFILE;
 613                         goto end;
 614                 }
 615         }
 616
 617         user_ret = open(user_data, out_fds);
 618         if (user_ret) {
 619                 ret = user_ret;
 620                 goto end;
 621         }
 622
 623         /*
 624          * Add the fds returned by the user's callback to the hashtable
 625          * of unsuspendable fds.
 626          */
 627         for (i = 0; i < fd_count; i++) {
 628                 struct unsuspendable_fd *entry = unsuspendable_fd_create(
 629                                 names ? names[i] : NULL, out_fds[i]);
 630
 631                 if (!entry) {
 632                         ret = -1;
 633                         goto end_free_entries;
 634                 }
 635                 entries[i] = entry;
 636         }
 637
 638         rcu_read_lock();
 639         for (i = 0; i < fd_count; i++) {
 640                 struct cds_lfht_node *node;
 641                 struct unsuspendable_fd *entry = entries[i];
 642
 643                 node = cds_lfht_add_unique(tracker->unsuspendable_fds,
 644                                 hash_key_ulong((void *) (unsigned long)
 645                                                                 out_fds[i],
 646                                                 seed.value),
 647                                 match_fd, (void *) (unsigned long) out_fds[i],
 648                                 &entry->tracker_node);
 649
 650                 if (node != &entry->tracker_node) {
 651                         ret = -EEXIST;
 652                         rcu_read_unlock();
 653                         goto end_free_entries;
 654                 }
 655                 entries[i] = NULL;
 656         }
 657         tracker->count.unsuspendable += fd_count;
 658         rcu_read_unlock();
 659         ret = user_ret;
 660 end:
 661         pthread_mutex_unlock(&tracker->lock);
 662         return ret;
 663 end_free_entries:
 664         for (i = 0; i < fd_count; i++) {
 665                 unsuspendable_fd_destroy(entries[i]);
 666         }
 667         goto end;
 668 }
 669
 670 int fd_tracker_close_unsuspendable_fd(struct fd_tracker *tracker,
 671                 int *fds_in,
 672                 unsigned int fd_count,
 673                 fd_close_cb close,
 674                 void *user_data)
 675 {
 676         int i, ret, user_ret;
 677         int fds[fd_count];
 678
 679         /*
 680          * Maintain a local copy of fds_in as the user's callback may modify its
 681          * contents (e.g. setting the fd(s) to -1 after close).
 682          */
 683         memcpy(fds, fds_in, sizeof(*fds) * fd_count);
 684
 685         pthread_mutex_lock(&tracker->lock);
 686         rcu_read_lock();
 687
 688         /* Let the user close the file descriptors. */
 689         user_ret = close(user_data, fds_in);
 690         if (user_ret) {
 691                 ret = user_ret;
 692                 goto end;
 693         }
 694
 695         /* Untrack the fds that were just closed by the user's callback. */
 696         for (i = 0; i < fd_count; i++) {
 697                 struct cds_lfht_node *node;
 698                 struct cds_lfht_iter iter;
 699                 struct unsuspendable_fd *entry;
 700
 701                 cds_lfht_lookup(tracker->unsuspendable_fds,
 702                                 hash_key_ulong((void *) (unsigned long) fds[i],
 703                                                 seed.value),
 704                                 match_fd, (void *) (unsigned long) fds[i],
 705                                 &iter);
 706                 node = cds_lfht_iter_get_node(&iter);
 707                 if (!node) {
 708                         /* Unknown file descriptor. */
 709                         WARN("Untracked file descriptor %d passed to fd_tracker_close_unsuspendable_fd()",
 710                                         fds[i]);
 711                         ret = -EINVAL;
 712                         goto end;
 713                 }
 714                 entry = caa_container_of(
 715                                 node, struct unsuspendable_fd, tracker_node);
 716
 717                 cds_lfht_del(tracker->unsuspendable_fds, node);
 718                 unsuspendable_fd_destroy(entry);
 719                 fds[i] = -1;
 720         }
 721
 722         tracker->count.unsuspendable -= fd_count;
 723         ret = 0;
 724 end:
 725         rcu_read_unlock();
 726         pthread_mutex_unlock(&tracker->lock);
 727         return ret;
 728 }
 729
 730 /* Caller must have taken the tracker's and handle's locks. */
 731 static void fd_tracker_track(
 732                 struct fd_tracker *tracker, struct fs_handle *handle)
 733 {
 734         if (handle->fd >= 0) {
 735                 tracker->count.suspendable.active++;
 736                 cds_list_add_tail(&handle->handles_list_node,
 737                                 &tracker->active_handles);
 738         } else {
 739                 tracker->count.suspendable.suspended++;
 740                 cds_list_add_tail(&handle->handles_list_node,
 741                                 &tracker->suspended_handles);
 742         }
 743 }
 744
 745 /* Caller must have taken the tracker's and handle's locks. */
 746 static void fd_tracker_untrack(
 747                 struct fd_tracker *tracker, struct fs_handle *handle)
 748 {
 749         if (handle->fd >= 0) {
 750                 tracker->count.suspendable.active--;
 751         } else {
 752                 tracker->count.suspendable.suspended--;
 753         }
 754         cds_list_del(&handle->handles_list_node);
 755 }
 756
 757 /* Caller must have taken the tracker's and handle's locks. */
 758 static int fd_tracker_restore_handle(
 759                 struct fd_tracker *tracker, struct fs_handle *handle)
 760 {
 761         int ret;
 762
 763         fd_tracker_untrack(tracker, handle);
 764         if (ACTIVE_COUNT(tracker) >= tracker->capacity) {
 765                 ret = fd_tracker_suspend_handles(tracker, 1);
 766                 if (ret) {
 767                         goto end;
 768                 }
 769         }
 770         ret = fs_handle_restore(handle);
 771 end:
 772         fd_tracker_track(tracker, handle);
 773         return ret ? ret : handle->fd;
 774 }
 775
 776 int fs_handle_get_fd(struct fs_handle *handle)
 777 {
 778         int ret;
 779
 780         /*
 781          * TODO This should be optimized as it is a fairly hot path.
 782          * The fd-tracker's lock should only be taken when a fs_handle is
 783          * restored (slow path). On the fast path (fs_handle is active),
 784          * the only effect on the fd_tracker is marking the handle as the
 785          * most recently used. Currently, it is done by a call to the
 786          * track/untrack helpers, but it should be done atomically.
 787          *
 788          * Note that the lock's nesting order must still be respected here.
 789          * The handle's lock nests inside the tracker's lock.
 790          */
 791         pthread_mutex_lock(&handle->tracker->lock);
 792         pthread_mutex_lock(&handle->lock);
 793         assert(!handle->in_use);
 794
 795         handle->tracker->stats.uses++;
 796         if (handle->fd >= 0) {
 797                 ret = handle->fd;
 798                 /* Mark as most recently used. */
 799                 fd_tracker_untrack(handle->tracker, handle);
 800                 fd_tracker_track(handle->tracker, handle);
 801         } else {
 802                 handle->tracker->stats.misses++;
 803                 ret = fd_tracker_restore_handle(handle->tracker, handle);
 804                 if (ret < 0) {
 805                         handle->tracker->stats.errors++;
 806                         goto end;
 807                 }
 808         }
 809         handle->in_use = true;
 810 end:
 811         pthread_mutex_unlock(&handle->lock);
 812         pthread_mutex_unlock(&handle->tracker->lock);
 813         return ret;
 814 }
 815
 816 void fs_handle_put_fd(struct fs_handle *handle)
 817 {
 818         pthread_mutex_lock(&handle->lock);
 819         handle->in_use = false;
 820         pthread_mutex_unlock(&handle->lock);
 821 }
 822
 823 int fs_handle_unlink(struct fs_handle *handle)
 824 {
 825         int ret;
 826
 827         pthread_mutex_lock(&handle->tracker->lock);
 828         pthread_mutex_lock(&handle->lock);
 829         ret = lttng_inode_defer_unlink(handle->inode);
 830         pthread_mutex_unlock(&handle->lock);
 831         pthread_mutex_unlock(&handle->tracker->lock);
 832         return ret;
 833 }
 834
 835 int fs_handle_close(struct fs_handle *handle)
 836 {
 837         int ret = 0;
 838         const char *path = NULL;
 839
 840         if (!handle) {
 841                 ret = -EINVAL;
 842                 goto end;
 843         }
 844
 845         pthread_mutex_lock(&handle->tracker->lock);
 846         pthread_mutex_lock(&handle->lock);
 847         if (handle->inode) {
 848                 path = lttng_inode_get_path(handle->inode);
 849         }
 850         fd_tracker_untrack(handle->tracker, handle);
 851         if (handle->fd >= 0) {
 852                 /*
 853                  * The return value of close() is not propagated as there
 854                  * isn't much the user can do about it.
 855                  */
 856                 if (close(handle->fd)) {
 857                         PERROR("Failed to close the file descritptor (%d) of fs handle to %s, close() returned",
 858                                         handle->fd, path ? path : "Unknown");
 859                 }
 860                 handle->fd = -1;
 861         }
 862         if (handle->inode) {
 863                 lttng_inode_put(handle->inode);
 864         }
 865         pthread_mutex_unlock(&handle->lock);
 866         pthread_mutex_destroy(&handle->lock);
 867         pthread_mutex_unlock(&handle->tracker->lock);
 868         free(handle);
 869 end:
 870         return ret;
 871 }